Vanadium bipyridine complex as well as preparation method and application thereof

Abstract

The invention discloses a vanadium dipyridyl complex, the chemical formula of the vanadium dipyridyl complex is V (bipyalk) (CH3OH) Cl3, and bipyalk is 2, 2 '-([2, 2'-dipyridyl]-6, 6 '-dimethyl) bis (propyl-2-alcohol), and the vanadium dipyridyl complex is prepared by the following steps: (1) adding bipyalk and vanadium trichloride into a first solvent, and reacting to obtain a mixture of a crude sample; and (2) concentrating the mixture of the crude sample, then diffusing a second solvent into the concentrated mixture of the crude sample, and crystallizing to obtain the vanadium bipyridine complex. The method provided by the invention can catalyze unpurified epoxide and cyclic anhydride to copolymerize in the air atmosphere to prepare polyester, and can effectively reduce the commercial production cost of polyester. The obtained polymer is high in selectivity (polyester chain link gt; the molecular weight is proper, and the molecular weight distribution is narrow.

Description

Technical Field

[0001] The invention relates to the field of coordination compounds, and in particular to a vanadium bipyridine complex and a preparation method and application thereof. Background Art

[0002] Since current commercial polyesters are usually prepared by condensation of diacids or diesters with diols (e.g. ethylene terephthalate), this process requires the removal of small molecule byproducts such as water or alcohol. The main problem with this step-by-step polymerization process is that it needs to be carried out under high temperature and vacuum conditions (200-220°C, 0.1 mmHg). This method is very energy-intensive and cannot synthesize polyesters that are easily heat-recyclable, while making the application of volatile monomers more difficult.

[0003] The ring-opening polymerization (ROP) method of cyclic esters is an atom-economic alternative to step-wise polymerization reactions (e.g., polylactic acid). In ROP, a catalyst is used to open the ring of a cyclic monomer to produce a reaction center, which coordinates with a new cyclic monomer and inserts into the reaction center to form a longer chain. ROP of cyclic esters can be carried out under mild conditions (room temperature, atmospheric pressure) under the catalysis of an appropriate initiator / catalyst system, because the active center reduces the reaction energy barrier and the process does not require the removal of small molecule byproducts. However, the ring opening is driven by the enthalpy generated by the release of ring stress, which limits its monomer range (mainly 4-, 6-, and 7-membered rings, and 5-membered rings are difficult to open and polymerize due to their small ring strain).

[0004] The ring-opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides is also an atom-economic reaction for the polyester chain growth pathway. At the same time, the process ΔH of each pair of epoxy and cyclic anhydride inserted in ROAC is ≈ -30 kcal / mol. This means that ROAC, like ROP, can be carried out under mild conditions (25-110°C) under the catalysis of efficient and highly selective catalysts. At the same time, compared with the ROP of cyclic ester monomers, the ROAC process has another advantage that the structure and properties of the polymer can be adjusted by adjusting the raw materials. Due to its huge economic and environmental benefits, ROAC has attracted much attention in the field of polyester synthesis.

[0005] Although many catalysts for ROAC of anhydrides and epoxides have been developed, most of them are sensitive to oxygen and proton impurities (water, acid, alcohol, amine). Trace amounts of water in the air, unpurified anhydrides, epoxides and solvents will react with the anhydrides to produce acids during the reaction, causing the active intermediates of the catalyst to degrade into free ligands and metal ions, reducing or eliminating the catalytic activity. Therefore, the reaction often requires nitrogen protection, as well as careful purification and dehydration of the anhydrides, epoxides and solvents before the reaction. For example, most literatures require the anhydrides to be sublimated or sublimated multiple times before the experiment, and the epoxides need to be stirred in calcium hydride for 1-3 days and then distilled. Even catalysts or co-catalysts with very small amounts need to be recrystallized multiple times or produced and stored under a nitrogen protection atmosphere. These operations will increase production costs, resulting in the need to increase the cost of raw material purification and nitrogen protection for polyester produced by ROAC in the process of competing with polyesters sold on the market, making it difficult to commercialize. Summary of the invention

[0006] In order to solve the problem that the existing epoxide and cyclic anhydride ring-opening copolymerization catalyst ROAC is deactivated in the presence of proton impurities and oxygen, making it difficult to reduce production costs, the present invention provides a vanadium bipyridine complex and a preparation method and application thereof.

[0007] The technical solution adopted by the present invention is:

[0008] A vanadium bipyridine complex, the chemical formula of which is V(bipyalk)(CH3OH)Cl3, wherein bipyalk is 2,2'-([2,2'-bipyridine]-6,6'-dimethyl)bis(propan-2-ol), and the chemical structural formula is:

[0009]

[0010] The present invention provides a method for preparing the above-mentioned vanadium bipyridine complex, comprising the following steps:

[0011] (1) adding bipyalk and vanadium trichloride to a first solvent to react to obtain a mixture of a crude sample;

[0012] (2) concentrating the crude sample mixture, and then diffusing a second solvent into the concentrated crude sample mixture to obtain a vanadium bipyridine complex after crystallization.

[0013] The above process is preferably carried out in a light-proof environment to prevent the trivalent vanadium from being oxidized by impurities in the solvent, thereby further improving the reaction yield.

[0014] In step (2), the crude sample mixture can be concentrated by conventional reduced pressure distillation.

[0015] Preferably, the organic solvent is at least one of methanol and ethanol.

[0016] Preferably, in step (1), the molar ratio of vanadium trichloride to bipyalk is 1-4:1, and more preferably 2-3:1. This can improve the reaction efficiency while ensuring the quality of the product obtained. Excessive vanadium trichloride is conducive to the complete reaction of bipyalk, reduces bipyalk consumption, and reduces production costs.

[0017] Preferably, in step (1), the molar ratio of the first solvent to bipyalk is 250-1000: 1, and more preferably, the molar ratio is 7000-8000: 1. An appropriate amount of the first solvent can completely dissolve vanadium trichloride, while reducing the use of solvent and accelerating the reaction rate.

[0018] Preferably, the second solvent is anhydrous ether, and the second solvent with low polarity is added to the first solvent with high polarity to effectively precipitate single crystals; wherein the molar ratio of anhydrous ether to bipyalk is 12.5-200:1, and the concentration of vanadium bipyridine complex at this molar ratio is close to its saturated solution concentration, which can effectively reduce the difficulty of single crystal growth and improve production efficiency.

[0019] Preferably, in step (1), the reaction temperature is 25-80° C.; in step (2), the crystallization temperature is -20-50° C. This can improve the reaction efficiency and ensure the quality of the obtained product.

[0020] The present invention also provides an application of the vanadium bipyridine complex as a catalyst in the copolymerization reaction of epoxide and cyclic anhydride.

[0021] The specific method includes: using epoxide and cyclic acid anhydride as raw materials, using vanadium bipyridine complex as catalyst, using onium salt or heterocyclic nitrogen base as co-catalyst, catalyzing the polymerization of cyclic acid anhydride and propylene oxide in toluene to prepare polyester.

[0022] Preferably, the cyclic anhydride is at least one of maleic anhydride, succinic anhydride, phthalic anhydride and nadic anhydride. The molecular weight distribution of the reaction product is narrower.

[0023] Preferably, the onium salt is selected from bis(triphenylphosphorane)ammonium chloride (PPNCl); the heterocyclic nitrogen base is selected from 4-dimethylaminopyridine (DMAP). The reaction rate is faster and the molecular weight distribution of the reaction product is narrower.

[0024] Preferably, the polymerization temperature is 80-100° C. Within this temperature range, the catalyst has higher activity, while reducing the occurrence of transesterification side reactions and maintaining a narrow molecular weight distribution.

[0025] Beneficial effects of the present invention:

[0026] 1. When the vanadium bipyridine complex of the present invention is used as a catalyst, because its bipyridine part is more stable than the traditional salen ligand, and the dimethyl group of the side chain effectively prevents the oxidation of the catalyst center ion, it can catalyze the copolymerization of unpurified epoxide and cyclic anhydride to prepare polyester under atmospheric atmosphere, which can effectively reduce the commercial production cost of polyester. The molecular weight of the obtained polyester is 1-6kDa, and the molecular weight distribution is 1.04-1.3. The present invention has the characteristics of high selectivity (polyester chain>90%), appropriate molecular weight, and narrow molecular weight distribution.

[0027] 2. The preparation method of the vanadium bipyridine complex of the present invention is simple and has high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a single crystal test image of the vanadium bipyridine complex of the present invention.

[0029] Figure 2 The polyester obtained in Example 7 1 H NMR spectrum.

[0030] Figure 3 The polyester obtained in Example 10 1 H NMR spectrum.

[0031] Figure 4 The polyester obtained in Example 11 1 H NMR spectrum.

[0032] Figure 5 The polyester obtained in Example 12 1 H NMR spectrum.

[0033] Figure 6 This is the GPC curve of the polyester obtained in Example 11 (35°C, THF as the mobile phase). DETAILED DESCRIPTION

[0034] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0035] The instrument used for single crystal testing of vanadium bipyridine complex is: Bruker D8 Venture.

[0036] The polymer product 1 The HNMR test instrument is: Bruker Avance NEO 500MHz, Germany.

[0037] Gel permeation chromatography (GPC) was determined using a Malvern Viscotek GPC / SEC workstation. The test method was as follows: the test sample concentration was 2 mg / mL, the injection volume was 100 uL, the column temperature was 35 °C, and the mobile phase was THF. Polystyrene (PSt) was used as the characterization sample, and the flow rate was set to 1.0 mL / min. After the sample was dissolved, the transition metal ions were adsorbed using neutral alumina, and then filtered using a 0.22 um filter membrane.

[0038] Example 1

[0039] Dissolve 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 20 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 50°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.1 mol (10 mL) of anhydrous ether into the concentrated liquid, and recrystallize it at 25°C in a dark environment. Vacuum dry the recrystallized solid to obtain about 308 mg of vanadium bipyridine complex. The yield is about 71%, and the single crystal test results are shown in Figure 1 .

[0040] Example 2

[0041] Dissolve 1 mmol (157 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 20 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 50°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.2 mol (20 mL) of anhydrous ether into the concentrated liquid, and recrystallize it at 25°C in a dark environment. Vacuum dry the recrystallized solid to obtain about 201 mg of vanadium bipyridine complex. The yield is about 47%, and the single crystal test results are shown in Figure 1 .

[0042] Example 3

[0043] Dissolve 4 mmol (629 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 20 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 50°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.05 mol (5 mL) of anhydrous ether into the concentrated liquid, and recrystallize it under light at 25°C. The recrystallized solid is vacuum dried to obtain about 189 mg of vanadium bipyridine complex. The yield is about 44%, and the single crystal test results are shown in Figure 1 .

[0044] Example 4

[0045] Dissolve 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 40 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 50°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.1 mol (10 mL) of anhydrous ether into the concentrated liquid, and recrystallize at 25°C in the dark. The recrystallized solid is vacuum dried to obtain about 230 mg of vanadium bipyridine complex. The yield is about 53%, and the single crystal test results are shown in Figure 1 .

[0046] Example 5

[0047] Dissolve 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 20 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 80°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.1 mol (10 mL) of anhydrous ether into the concentrated liquid, and recrystallize it under light at 50°C. The recrystallized solid is vacuum dried to obtain about 129 mg of vanadium bipyridine complex. The yield is about 30%, and the single crystal test results are shown in Figure 1 .

[0048] Example 6

[0049] Dissolve 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk in 20 mL of methanol, and slowly drip the obtained methanol solution of vanadium trichloride into the obtained methanol solution of the ligand. Stir and heat the system to 25°C in a closed system for 5-6 hours. After the reaction is completed, use a rotary evaporator to concentrate the liquid to 2-4 mL, diffuse 0.1 mol (10 mL) of anhydrous ether into the concentrated liquid, and recrystallize at -20°C in a dark place. Vacuum dry the recrystallized solid to obtain about 140 mg of vanadium bipyridine complex. The yield is about 35%, and the single crystal test results are shown in Figure 1 .

[0050] Example 7

[0051] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 1, 8 μmol of DMAP, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 80°C, reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was obtained by GPC (gel permeation chromatography) test. The results are shown in Figure 2 , the product molecular weight and molecular weight distribution were obtained, and the results are shown in Table 1.

[0052] Example 8

[0053] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 2, 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 80°C, reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was dried under vacuum to obtain the pure polyester. The pure polyester was tested by GPC (gel permeation chromatography) to obtain the product molecular weight and molecular weight distribution. The test results are shown in Table 1.

[0054] Example 9

[0055] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 3, 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 100°C, reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield and polyether fragment content of the polyester were obtained by H NMR characterization. The concentrated crude product was dissolved in 2-4 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was vacuum dried to obtain the pure polyester. The pure polyester was tested by GPC (gel permeation chromatography) to obtain the product molecular weight and molecular weight distribution. The test results are shown in Table 1.

[0056] Example 10

[0057] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 4, 1.44 mmol of maleic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 100°C, reacted for 16 hours, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was obtained by GPC (gel permeation chromatography) test. The results are shown in Figure 3 , the product molecular weight and molecular weight distribution were obtained, and the results are shown in Table 1.

[0058] Embodiment 11

[0059] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 5, 8 μmol of PPNCl, 1.44 mmol of nadic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 100°C, reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was obtained by GPC (gel permeation chromatography) test and GPC curve analysis. The results are shown in Figure 4 and Figure 6 , the product molecular weight and molecular weight distribution were obtained, and the results are shown in Table 1.

[0060] Example 12

[0061] In an air atmosphere, 4 μmol of the vanadium bipyridine complex prepared in Example 6 and 4 μmol of the vanadium bipyridine complex prepared in Example 7, 8 μmol of PPNCl, 1.44 mmol of phthalic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, and the bottle was sealed with a polytetrafluoroethylene-lined lid, heated to 100° C., reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times. The pure polyester was obtained by GPC (gel permeation chromatography) test. The results are shown in Figure 5 , the product molecular weight and molecular weight distribution were obtained, and the results are shown in Table 1.

[0062] Comparative Example 1

[0063] According to the literature Alkali Metal Carboxylates: Simple and Versatile Initiators for Ring-Opening Alternating Copolymerization of Cyclic Anhydrides / Epoxides; Chong-Min Chen, Xiaowei Xu, He-Yuan Ji, Bin Wang, Li Pan, Yi Luo, and Yue-Sheng Li; Macromolecules 2021 54(2), 713-724; DOI: 10.1021 / acs.macromol.0c02389, it is reported that potassium acetate can be used to catalyze the copolymerization of epoxides and cyclic anhydrides.

[0064] In an air atmosphere, 8 μmol potassium acetate, 1.44 mmol succinic anhydride, 320 mmol toluene, and 2.88 mmol propylene oxide were added to the test bottle in sequence, sealed with a polytetrafluoroethylene-lined lid, heated to 100°C, and reacted for 16 hours. After the reaction, the product was completely dissolved in ethanol, indicating that there was no product or the product was an oligomer.

[0065] Comparative Example 1 shows that although alkali metal carboxylates can catalyze the polymerization of propylene oxide and cyclic anhydride, the polymerization results in air atmosphere are far from satisfactory.

[0066] Comparative Example 2

[0067] In an air atmosphere, 8 μmol potassium acetate, 8 μmol PPNCl, 1.44 mmol succinic anhydride, 320 mmol toluene, and 2.88 mmol propylene oxide were added to the test bottle in sequence, sealed with a polytetrafluoroethylene-lined lid, heated to 100 °C, reacted for 16 h, and the reaction product was concentrated and the crude reaction product was subjected to 1 The yield of polyester and the content of polyether fragments were characterized by H NMR. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured out, and the dissolution, precipitation and washing were repeated three times, and the pure polyester was obtained by vacuum drying.

[0068] The obtained pure polyester was subjected to GPC (gel permeation chromatography) test to obtain the product molecular weight and molecular weight distribution, and the conversion rate was only 25%. At the same time, the product was an oligomer, and no peak with a molecular weight higher than 500 was observed in the GPC test. Comparative Example 2 shows that even if a co-catalyst is additionally added, the alkali metal carboxylate does not perform well.

[0069] Comparative Example 3

[0070] (1) According to the literature Ring-Opening Copolymerization of Maleic Anhydride with Epoxides: A Chain-Growth Approach to Unsaturated Polyesters; Angela M. DiCiccio and Geoffrey W. Coates; Journal of the American Chemical Society 2011 133(28), 10724-10727; DOI: 10.1021 / ja203520p, a chromium complex was prepared.

[0071] (2) In an air atmosphere, 8 μmol of the chromium complex obtained in step (1), 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, sealed with a polytetrafluoroethylene-lined lid, heated to 100° C., and reacted for 16 h. The complex quickly lost its activity, and the anhydride conversion rate was only 15%. At the same time, the conversion rate was too low to be purified for molecular weight testing. Comparative Example 3 shows that although these catalysts have better performance under nitrogen protection, they perform poorly in the presence of oxygen and proton compounds.

[0072] Comparative Example 4

[0073] (1) According to the literature Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation; Angela M. DiCiccio, Julie M. Longo, Gabriel G. Rodríguez-Calero, and Geoffrey W. Coates; Journal of the American Chemical Society 2016 138(22),7107-7113; DOI:10.1021 / jacs.6b03113 Preparation of aluminum complexes.

[0074] (2) In an air atmosphere, 8 μmol of the aluminum complex prepared in step (1), 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added to the test bottle in sequence, sealed with a polytetrafluoroethylene-lined lid, heated to 100° C., and reacted for 16 h. The complex quickly lost its activity, and the anhydride conversion rate was only 11%. At the same time, the conversion rate was too low to be purified for molecular weight testing. Comparative Example 4 shows that although these catalysts have better performance under nitrogen protection, they perform poorly in the presence of oxygen and proton compounds.

[0075] Table 1 Reaction conditions and results of Examples 7-12

[0076]

[0077] In Table 1, SA is succinic anhydride, MA is maleic anhydride, CPMA is nadic anhydride, and PA is phthalic anhydride. The abbreviations of the cocatalysts are: DMAP is 4-dimethylaminopyridine, and PPNCl is bis(triphenylphosphorane)ammonium chloride. The conversion rate and the polyether ratio are calculated by 1 The polyether content was determined by HNMR, but the raw material / product peak of nadic anhydride appeared at a chemical shift of about 3.5 ppm, so the polyether content could not be determined. The number average molecular weight, weight average molecular weight and molecular weight distribution index were determined by GPC.

[0078] It can be concluded from Table 1 that the vanadium bipyridine catalyst of the present invention has a good catalytic effect on the polymerization of various acid anhydrides and propylene oxide, indicating that the catalyst of the present invention has good catalytic activity and high universality. Even if an excess of propylene oxide is used, a large amount of propylene oxide homopolymerization will not occur, proving that the catalyst has high selectivity.

[0079] It can be concluded from Examples 7-12 and Comparative Examples 1-4 that the vanadium bipyridine catalyst prepared in the present invention has the property of tolerating proton impurities and oxygen, which is not possessed by other propylene oxide and cyclic anhydride copolymerization catalysts.

[0080] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the specific embodiments of the present invention can still be modified or some technical features can be equivalently replaced. Without departing from the spirit of the technical solutions of the present invention, they should be included in the scope of the technical solutions for which protection is sought in the present invention.

Claims

1. A vanadium bipyridine complex, characterized in that: Its chemical formula is V(bipyalk)(CH3OH)Cl3, where bipyalk is 2,2'-([2,2'-bipyridine]-6,6'-dimethyl)bis(propan-2-ol) and its chemical structure is:

2. The method for preparing the vanadium bipyridine complex according to claim 1, characterized in that: The following steps are involved: (1) adding bipyalk and vanadium trichloride to a first solvent to react to obtain a mixture of a crude sample; (2) concentrating the crude sample mixture, and then diffusing a second solvent into the concentrated crude sample mixture to obtain a vanadium bipyridine complex after crystallization.

3. The preparation method according to claim 2, characterized in that: The first solvent is at least one of methanol and ethanol.

4. The preparation method according to claim 2, characterized in that: In step (1), the molar ratio of vanadium trichloride to bipyalk is 1-4:1; and the molar ratio of the first solvent to vanadium trichloride is 250-1000:

1.

5. The preparation method according to claim 2, characterized in that: The second solvent is anhydrous ether, wherein the molar ratio of anhydrous ether to vanadium trichloride is 12.5-200:

1.

6. The preparation method according to claim 2, characterized in that: In step (1), the reaction temperature is 25-80°C; in step (2), the crystallization temperature is -20-50°C.

7. Use of the vanadium bipyridine complex according to claim 1 as a catalyst in the copolymerization reaction of epoxide and cyclic anhydride.

8. The use according to claim 7, characterized in that: include: The polyester is prepared by using epoxide and cyclic acid anhydride as raw materials, vanadium bipyridine complex as catalyst, onium salt or heterocyclic nitrogen base as co-catalyst, cyclic acid anhydride and propylene oxide are polymerized in toluene.

9. The use according to claim 8, characterized in that: The cyclic acid anhydride is at least one of maleic anhydride, succinic anhydride, phthalic anhydride and nadic anhydride.

10. The use according to claim 8, characterized in that: The onium salt is selected from bis(triphenylphosphorane)ammonium chloride; and the heterocyclic nitrogen base is selected from 4-dimethylaminopyridine.

11. The use according to claim 8, characterized in that: The polymerization temperature is 80-100°C.

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